<!DOCTYPE html> 
<html lang="en"> 
<head> 
<meta charset="UTF-8"> 
<meta name="viewport" content="width=device-width, initial-scale=1.0"> 
<title>const 命令声明常量值</title> 
<script> 
    const PI ; // = 3.1415926; 
    console.log(PI);
// const PI = 3.1415926; 
// console.log(PI); 
 PI = 3.14; // Uncaught TypeError: Assignment to constant variable. 
 </script> 
 </head> 
 <body></body> 
 </html> 